1. Field of This Invention
This invention relates to impact modifiers for PVC polymer compositions and PVC polymer compositions containing such impact modifiers.
2. Prior Art
While ABS is a styrene-acrylonitrile polymer matrix with a butadiene or butadiene copolymer elastomer component, ASA is a styrene-acrylonitrile matrix containing a polyacrylate elastomer. Both ABS and commercially available ASA materials are opaque, yellowish white molding materials. As to known acrylonitrile-styrene-acrylate ester thermoplastic compositions, see page 32 of Materials Guide, published by British Plastics, (Aug. 1971).
With the substitution of acrylate based elastomer for a butadiene based one, ASA plastics are claimed to have significantly higher photochemical, i.e., weathering and oxidative, resistance than ABS and, therefore, find major use outdoors. Published data, however, suggest, while ASA plastics do have higher photochemical stability, that ASA plastic show up to 8 to 10 times the exposure before loss of impact resistance is noted -- failure thereafter is precipitous. In ABS systems, due to the butadiene moieties present, degradation and crosslinking reaction occur simultaneously, giving rise to an initial and continuing decline in impact resistance and growing yellowing with time.
Attention is drawn to U.S. Pat. No. 3,448,175, Belgian Pat. No. 775,373, U.S. Pat. No. 3,681,475, Japanese Pat. No. 4,709,993 and U.S. Pat. No. 3,678,133.